1) Field of the Disclosure
The disclosure relates generally to devices and systems for generating electrical power, and more particularly, to thermoelectric devices and methods for generating electrical power.
2) Description of Related Art
Small sensors are used in a variety of applications in aircraft, spacecraft, motorcraft, watercraft, and other craft, as well as vehicles and structures. For example, an array of small sensors may be used in structural health monitoring (SHM) to continuously monitor structures, such as composite structures of aircraft, and measure material characteristics and stress and strain levels to assess performance, possible damage, and current state of the structure. A series of small sensors may also be used in aircraft for “fly-by-feel” applications to provide feedback to the flight controls to adjust the flight envelope or to limit loads in the flight pattern. Moreover, small sensors may be used with on-board wireless communication of controls on an aircraft, damage tolerant structures on an aircraft, and redundant power supplies for additional sources of power on an aircraft. The implementation of such small sensors in these applications can require the use of additional power and communication wires which can increase the complexity and costs. Thus, generating power locally, rather than from a central source, for these types of small sensor systems is desirable.
The harvesting of electricity from other forms of energy to drive small and mid-size sensor devices (between 100 milliwatts and 100 watts) is known. For example, solar panels have been used to harvest electricity. However, such solar panels can be costly to make and bulky in size. In addition, known power sources used with remote sensors can include vibration scavengers based on piezoelectric materials, which generate a voltage when deformed, and scavengers based on thermal gradients or thermoelectric junctions, which generate a voltage as a function of temperature. However, these known power sources can be bulky, can add weight, and can be difficult to harvest sufficient energy at a specific location of need.
Thermoelectric based generator devices have been found to be effective when used with aircraft and other craft because there are no moving parts and a thermal gradient is typically present. Thermoelectric devices can convert thermal energy directly into electrical power or electricity. The thermal gradient is applied across two faces of the device, as it is not sufficient to have a gradient across only one face. With thermoelectric devices, the power generated is dependent upon the change in temperature across the device itself.
Known thermoelectric devices and systems include add-on components rather than fully integrated structures. For example, the use of non-integrated thermoelectric based generator devices that may include exterior heat sinks and water cooling to increase the thermal gradients is known. However, such non-integrated thermoelectric based generator devices may not provide sufficient power for an extended period of time and may be heavy, thus increasing the overall weight of an aircraft. Moreover, in applications where locally generated power is required, the thermal gradient accessible to an add-on device is typically only 1% to 2%, resulting in the add-on device having decreased efficiency. For example, with an add-on device, only 1% of a 150° F. ΔT (temperature difference), or upwards of 250° F. ΔT on engine cowlings, or 2° F. ΔT can be used to generate thermoelectric power. This may be improved by adding other heat conducting or cooling materials, but this can result in the addition of significant weight, thus dropping the ratio of generated power per pound of additional weight.
In addition, the use of add-on power sources, such as vibration based energy harvesting units, is also known. However, such vibration based energy harvesting units can add weight to the aircraft, and they can protrude from the surrounding surface by ¼ inch to ½ inch, thus impacting the ability to implement them. Moreover, the use of add-on small, thin-film lithium batteries to harvest energy is also known. However, such small, thin-film lithium batteries can require increased maintenance.
Accordingly, there is a need in the art for an integrated thermoelectric composite structure and method that provides advantages over known devices and methods.